Photodiode imagers are well known in the art and are used in a great variety of devices including for example digital cameras, infrared detectors or imagers, x-ray imagers, etc. Generally, large area imagers, such as infrared and x-ray imagers, present a different problem than small area imagers, such as digital cameras. For example, because of the large sensing areas the substrate must be larger and heavier and connecting lines are longer and thicker so that coupling capacitances become larger and more problematic. Crystalline wafer over large size also becomes expensive or impractical. For example, image array for a chest x-ray device requires area of 400 mm×450 mm size, while the largest Si wafer nowadays is a round disk 300 mm in diameter, which can only be fabricated into a chip 200 mm×250 mm. That is to say, other than the cost factor, the dimension with silicon wafer could be limited from certain applications.
In the fabrication of large area imagers, there are generally two approaches. A first approach is to fabricate the photodiode array first (i.e. on the substrate) and to fabricate the pixel TFT electronics later. A second approach is to do the pixel TFT electronics on the substrate and to fabricate the photodiode array later. In each of these approaches there are several problems including the direction of illumination, interaction between metal contacts, the number of process steps, etc.
It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art.
Accordingly, it is an object of the present invention to provide a new and improved process for fabricating a pixelated imager with a metal-oxide thin film transistor (MOTFT) array.
It is another object of the present invention to provide a new and improved process for fabricating a pixelated imager using a fewer number of process steps.
It is another object of the present invention to provide a new and improved process for fabricating an imager in which coupling capacitance is substantially reduced.
It is another object of the present invention to provide a new and improved process for fabricating an imager in which the imager and MOTFET array interact to reduce the number of interconnections.
It is another object of the present invention to provide a new and improved process for fabricating large area imagers.
It is another object of the present invention to provide new and improved imagers and especially large area imagers.
It is another object of the present invention to provide a new and improved process for fabricating infrared imagers with more image pixels.